In these days, various kinds of waste water and contaminated water contaminate the rivers and soils, and how to handle this problem has become a serious matter. The waste water discharged from the homes of urban areas and the waste water discharged from factories and other facilities are doubling their seriousness everyday. Particularly, schools, tenting open fields, hot springs, golf courses, factory areas, cattle feces treating facilities, livestock waste material treating facilities and the like discharge large volumes of waste water to contaminate the rivers and soils. Therefore, an effective treatment of this waste water has become an urgent problem.
In treating the waste water, the biological method has been widely utilized so far. In the biological treatment method, microbes are utilized to make the contaminants decomposed, thereby lowering the BOD (biological oxygen demand). Generally, the conventional biological treating facility includes: a storage tank for temporarily storing the incoming waste water; an aeration tank for decomposing the organic materials by utilizing microbes; a sedimentation tank for precipitating the sludge; and a final storage tank for temporarily storing the treated water.
The biologically treated water is made to flow away to rivers and the sea, or it is treated for the second time before it is discharged to the rivers and the sea. In the biologically treated water, the organic substances are mostly eliminated, but considerable amounts of nitrogen and phosphorus remain. The remaining nitrogen and phosphorus synthesize organic matters such as vegetable plankton and moss, with the result that the green water is generated.
In order to remove nitrogen and phosphorus from the biologically treated water, there have been attempted various methods, but none of them has been successful so far. One of the attempted methods is that in which a second treatment is carried out by employing a sand filtering and an active filtering. In this method, however, various disadvantages are accompanied such as a low treatment efficiency, a high operating and facility cost, and a fastidious operating technique. Therefore, this method could not be put to the practical use. In another method, special plants such as dropworts or the like are experimentally tried. For example, dropworts are planted in a wide wet field to make the dropworts absorb nitrogen or phosphorus components. Or other plants are planted for the same purpose. In this method, however, the treatment efficiency is low, and furthermore, these plants are withered to death in winter seasons. Thus this method has been proved to be not reliable.
In this context, the present inventor has developed a system which can be added to the biologically treating facility to remove the remaining nitrogen and phosphorus components.